Cylindrospermopsis raciborskii is a toxic cyanobacterium found in fresh and weakly brackish water. It is believed to be native to tropical regions in Asia or tropical America, and dispersed poleward by natural vectors, such as migratory birds, and human vectors such as ballast water. The range expansion may be favored by climate change. Cylindrospermopsis produces toxins, cylindrospermopsin which can cause liver damage in humans, and saxitoxin, a neurotoxin. Blooms of Cylindrospermopsis have been associated with a decline in zooplankton abundance. Estuarine blooms of C. raciborskii have been reported in the Caernavon-Breton Sound estuary, Louisiana, the St. Johns River, Florida, the Neuse estuary, North Carolina, and Chesapeake Bay.